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What are Gonadorelin analogues (Zoladex®  or Prostap®) used to treat?  

Gonadorelin analogues are used in the treatment of:-

  • Endometriosis.
  • Shrinking of fibroids prior to surgery.
  • Thinning of the lining of the womb (Endometrium) before surgery
  • Pelvic pain 
  • As a temporary measure to stop bleeding/heavy periods.
  • Severe pre-menstrual syndrome (this is not usually as first line). 
  • Assisted reproduction such as in vitro fertilisation (IVF)

How the Treatment works:

The treatment works to stop your periods temporarily, by blocking the hormones that cause ovulation to occur.  This stops Oestrogen production by the ovary.  By stopping the Oestrogen, this stops the stimulation of the growth of fibroids or  endometrial deposits so they can shrink and reduces the thickening of the lining of the womb by preventing regeneration. This is either enough on its own to help the condition or helps to improve the results of surgery.  The blood and hormone supply to the pelvis is reduced and it is this that is thought to help in pelvic pain. 

Receiving your Treatment:

What is used:

We commonly use injections with trade names of Zoladex or Prostap. 

How it is given:

oladex is given as an injection by your doctor or a nurse and takes only a few seconds. It is inserted into the tummy fat whilst you are lying on a couch Prostap is injected into the upper arm or buttock.  

Timing of treatments:

It is important that the treatment is continued every 28 days for 3.6mg or every 12 weeks for Zoladex 10.8mg.  If the gap between treatments is longer, then annoying breakthrough bleeding can occur.  

Given in hospital and by GP surgery:

Zoladex may be started in the hospital outpatient clinic or GP surgery, but all the next doses will be continued at your GP surgery, either by your doctor or a clinic nurse.  Once you’ve had your first dose, please ensure that you have made an appointment for 28 days’ time with your doctor’s surgery.  Do not leave it until the last minute.

Add back HRT

You can be given add back HRT in the form of low dose of Oestrogen.  This gives a steady low dose to the whole body to reduce the side effects caused by the temporary lowering of oestrogen in the blood. This is given to take every day once the course of GnRH injections has started.

Side Effects

Do not be alarmed by this list of possible side effects, you may not experience any of them.  

Very common side effects means that more than 10% of people are affected

  • Hot flushes and sweating
  • Reduced sex drive
  • Vaginal dryness
  • Changes in breast size
  • Common side effects affect 1-10% of people:
  • Headaches
  • Depressed mood.
  • Tingling in the fingers or toes
  • Skin rash. 
  • Reaction at the site of injection and decreased bone density (If used for over six months)
  • You may get breast tenderness and vaginal bleeding in the few months, this is normal and after the first and second month of treatment this should cease.  
  • If you have fibroids a slight increase in symptoms such as pain may occur. 
  • For many patients with pelvic pain it may take 2 months before the symptoms have receded enough for you to feel relief.  

All these side effects are usually short lived and stop    after the second treatment. If any of these side effects become troublesome, speak with your doctor.  

Very rare (less than one in ten thousand) but important to seek help side effect:

The injection can affect the pituitary gland in your brain causing severe headaches, sickness affecting your vision and in more serious cases causing unconsciousness.  

Please tell your nurse or doctor if you are having these problems.

Long Term side effects:

This medicine can cause a small loss of calcium from the bones (thinning of the bones).  If you remain on treatment for more than 6 months you will require add back oestrogen to help maintain bone strength.  Some recovery of this loss occurs when treatment is stopped.  If you are suffering from any disease which affects the strength of your bones, check that your doctor is aware of it.

Frequent Asked Questions

Can I still work and drive after having the treatment?

After the injection you would expect to continue on with your daily activities with no immediate problems. The injection is unlikely to affect your ability to drive a car or operate machinery.

If you get any other undesirable events or think your medicine is causing any problems, tell your doctor or pharmacist. Please ensure your doctor knows all the medications that you are using so they can check there is no cross reaction.

What if I don’t like injections?

We commonly use the preparation Zoladex in the department. This is because its administration is swift and easy, minimising the discomfort during the injection.
 
Alternatives: You may be advised about surgical alternatives or other medical options such as Ryeqo tablets for your gynaecological problems. These work differently and may not be as suitable for you. This should be discussed further with your consultant. 

Can I get pregnant on this treatment?

Even when your periods have stopped there is an increased risk of getting pregnant on this injection. It is therefore advised that whilst receiving Gonadorelin analogue, barrier methods of contraception such as the condom or diaphragm (the cap) or a coil should be used.

When is a Gonadorelin analogue not given?

  • If you are pregnant or trying to become pregnant (accept where part of the treatment is for infertility)
  • If you have previously had an allergic reaction to this type of medicine
  • If you are breastfeeding

Caring for your medicine

You may be required to get a prescription from the pharmacist to bring to the surgery.  Once you have  collected your medication from the pharmacy, keep it in it’s original package, don’t break the seal and do not store it above 25 degrees. Keep it in a safe place here children cannot see it or reach it. Take it to the clinic for your appointment.

If you have problems e.g. side effects being more severe than you expected or irregular bleeding not settling after the second injection, make an appointment with your GP to discuss continuing, being prescribed add back HRT or alternatives.

Once the treatment is over:

  • The effect of the treatment should wear off over 4-6 weeks. 
  • If you have had surgery as well, the success of the surgery can be seen after this time. 
  • If you are wanting your periods to return this normally takes 4-6 weeks. 
  • Rarely they takes longer to return or further treatment is needed to re start ovulation. 
  • Even more rarely a woman has gone through an early menopause at the time of the injections. The injections did not cause this. 
  • Occasionally small cysts (swelling on the ovaries) can occur following the use of GnRH analogues. They may cause pain for some women.  These cysts usually disappear without treatment. If you are wanting your periods to return this normally takes 4-6 weeks. Rarely they takes longer to return or further treatment is needed to re start ovulation. 
  • Even more rarely a woman has gone through an early menopause at the time of the injections. The injections did not cause this. 
  • Occasionally small cysts (swelling on the ovaries) can occur following the use of GnRH analogues. They may cause pain for some women.  These cysts usually disappear without treatment.

References and additional resources

Contact us

If you have any queries relating to this information, please contact the Gynaecology service.

About this information

Service:
Gynaecology

Reference:
L/012

Approval date:
29 May 2026

Review date:
1 May 2029

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